Presence of mollusk assemblages was studied within red coralligenous algae Corallina officinalis L. along the southern Istrian coast. C. officinalis turfs can be considered a biodiversity reservoir, as they shelter numerous invertebrate species. The aim of this study was to identify mollusk species within these settlements using DNA barcoding as a method for detailed identification of mollusks. Nine locations and 18 localities with algal coverage range above 90% were chosen at four research areas. From 54 collected samples of C. officinalis turfs, a total of 46 mollusk species were identified. Molecular methods helped identify 16 gastropod, 14 bivalve and one polyplacophoran species. COI sequences for two bivalve species (Musculus cf. costulatus (Risso, 1826) and Gregariella semigranata (Reeve, 1858)) and seven gastropod species (Megastomia winfriedi Peñas & Rolán, 1999, Eatonina sp. Thiele, 1912, Eatonina cossurae (Calcara, 1841), Crisilla cf. maculata (Monterosato, 1869), Alvania cf. carinata (da Costa, 1778), Vitreolina antiflexa (Monterosato, 1884) and Odostomia plicata (Montagu, 1803)) represent new BINs in BOLD database. This study contributes to new findings related to the high biodiversity of mollusks associated with widespread C. officinalis settlements along the southern coastal area of Istria.

Market demand for scallops has considerably increased in recent decades. Although natural populations of scallops are vulnerable, the queen scallop, Aequipecten opercularis, can represent a possible alternative to at-risk species. The aim of this study was to determine the effect of seawater parameters on the commercial quality, biological indices and nutritional quality of the scallop A. opercularis in 1900 L tanks in ex situ conditions. The condition index (CI) and meat yield (MY) peaked in autumn (89.92% and 40.29%, respectively). The muscle index (MI) showed the highest peak during the winter season (5.96%), while the gonadosomatic index (GSI) (34.06%) peaked in the spring months. Protein content (6.89–9.56 g/100 g), lipids (2.58–2.79 g/100 g) and carbohydrates (0.12–0.33 g/100 g) varied during the study period. Seasonal fluctuations in seawater temperature and pH negatively influenced the CI, MY and protein and lipid content, while positively affecting carbohydrate and moisture content. The most suitable period of the year for the consumption of the scallop A. opercularis was found to be the winter and spring periods, when the scallops achieved their highest nutritional value. It can be stated from this study that queen scallops in the Adriatic Sea have a high nutritional quality and that they can be proposed for higher human consumption.